Markups tend to take place in the stocks that have been the best performers during the quarter (all data refer to Q3):

Number of of S&P stocks up more than 20% during the quarter: 35Number that showed a gain in last three days of quarter: 28Percentage of stocks that showed a "markup": 80%Number of S&P stocks down more than 15% in the quarter: 30Number that showed gains in last three days of quarter: 14Percentage of stocks that showed a "markup": 47%

So, there is some statistical evidence that strong stocks saw quarter-end markups Q3, while the weaker ones did not.